Respiratory system of insects

These external openings, which act as muscular valves in some insects, lead to the internal respiratory system, a densely networked array of tubes called tracheae.

It is responsible for delivering sufficient oxygen (O2) to all cells of the body and for removing carbon dioxide (CO2) that is produced as a waste product of cellular respiration.

At the same time, carbon dioxide, produced as a waste product of cellular respiration, diffuses out of the cell and, eventually, out of the body through the tracheal system.

To prevent its collapse under pressure, a thin, reinforcing "wire" of cuticle (the taenidia) winds spirally through the membranous wall.

This design (similar in structure to a heater hose on an automobile or an exhaust duct on a clothes dryer) gives tracheal tubes the ability to flex and stretch without developing kinks that might restrict air flow.

In dry terrestrial environments, this temporary air supply allows an insect to conserve water by closing its spiracles during periods of high evaporative stress.

Small insects rely almost exclusively on passive diffusion and physical activity for the movement of gases within the tracheal system.

[2] Periods in Earth's ancient history, however, such as the Carboniferous, featured much higher oxygen levels (up to 35%) that allowed larger insects, such as meganeura, along with arachnids, to evolve.